As U.S. children are exposed to 8½ hours of TV, video games, computers and other media a day — often at once — are they losing the ability to concentrate?

Are their developing brains becoming hard-wired to "multi-task lite" rather than learn the focused critical thinking needed for a democracy?

These troubling questions are raised by a Kaiser Family Foundation media study this month, says educational psychologist David Walsh of the National Institute on Media and the Family, a Minneapolis non-profit. Even more troubling is the answer: We don't know, Walsh and other experts in the field say.

Teachers and school psychologists notice that more kids than ever won't sit still. "I hear it all the time," says Walsh, who does more than 150 workshops on media a year for parents and educators. "It's become harder over the last 10 years to keep kids' attention. The expectation is to be constantly entertained and, if they're not entertained, they quickly lose interest."

The problem intensifies after third grade, when harder course work requires children to concentrate, adds Susan Ratteree, who supervises other public-school psychologists in suburban New Orleans. Diagnoses of attention-deficit hyperactivity disorder (ADHD) "have gone through the roof," she says. Though the disorder is more recognized these days, children seem to be different too, "and many teachers think the fast-paced media is having an effect."

Many sides of multi-tasking

Children are more attuned to distractions around them. "They attend to everything — the air vents creaking, someone talking. They bounce from task to task. Teachers here say kids have more trouble getting organized, and their attention spans are not as good as they used to be," says school psychologist Tamara Waters-Wheeler of the Bismarck-Mandan, N.D., public schools.

Studies with college students and adults show that the brain doesn't work as well when it focuses on more than one task, Walsh says. If the challenge demands a lot of attention, mental performance is particularly poor. But he says there are no such studies on today's kids as they multi-task with new media — instant-messaging, plugged into an iPod and doing homework at the same time.

And some evidence suggests that children's brains might be changing so they can juggle and concentrate better than their elders.

Scores on intelligence tests have been steadily rising since the 1940s, says University of Utah neuropsychologist Sam Goldstein. The tests measure a child's ability to shift and divide attention, but they also cover problem-solving and comprehension skills. "They're smarter," Goldstein says.

Another germane fact: In the Kaiser study, computer use and TV didn't seem to affect grades, but more time playing video games and less time reading were linked to poorer grades. About half of kids have a video game player in their rooms; more than two-thirds have TV sets.

Even parents who try hard to control their children's media use can have a rough time of it. Ella Serebryannik, 41, of Irvine, Calif., a computer programmer, works 7 a.m. to 4 p.m. so she can be with her two boys after school. Still, she says, "it's a constant fight" to limit their media exposure.

They aren't allowed any TV on school days and are supposed to watch only an hour a day on weekends. But 11-year-old Joshua wakes up at 6 a.m. on the weekends to watch cartoons as his parents sleep. "Concentration? No problem. He doesn't hear, he doesn't see, he tunes out everything when he watches TV. He can watch for hours and hours. He's addicted."

Sasha, 16, listens to music and instant-messages his friends as he does homework. "And now I'm looking for a math tutor for him," she adds. "I could enforce the rules more," she concedes. "It's just that we're picking our battles." Both boys read a lot and like theater, "but I'm concerned about how all this media is affecting their lives."

A need to be 'media literate'

Violent video games and TV have been shown to encourage aggressive behavior, says Michael Rich, a Harvard pediatrician and director of the Center on Media and Child Health in Boston. Also, the more TV watched, the more overweight a kid is likely to be, he says.

"We have so little good research on children and media, but what we have is concerning," Rich says. There are few "media literacy" programs in schools to help children sort out advertising claims and understand how media can affect them, Rich says.

Bipartisan legislation introduced in the Senate this month would spend $10 million in federal money the first year and $90 million over five years to research how electronic media affect the mental, social, physical and psychological development of children.

Very large studies on the question are needed, Goldstein says. Meanwhile, kids are growing up. "Our society isn't driven by finding out what we don't know; it's driven by the dollar. If it sells and doesn't kill anybody the first week, nobody takes a closer look."

We need the studies, but parents need to step up with more than rules alone, Goldstein emphasizes.

"The solution isn't to build taller walls and stronger locks to keep the world away, but to teach children how to make good choices."